Locating Objects in Space

Constellations 88 constellations in the night sky 28 northern hemisphere, 12 zodiac, 48 southern hemisphere Used as navigational guide Each culture has different names, all recognize the same star groupings Greek letters are used for identifying the brightest stars in constellations  Alpha  Beta γ Gamma Bright Dim

Reference Points Zenith – point directly above you in the sky Celestial Sphere – imaginary sphere surrounding the earth on which the stars are located (Stars only appear to be on celestial sphere) Celestial Poles – extensions of earth’s geographic poles (North Pole – Polaris…the pole star) Celestial Equator – extension of Earth’s equator Ecliptic – apparent path of the sun on the celestial sphere

Celestial Coordinates: “directions” to help you find objects in the night sky Declination: degrees North & South of the celestial equator *like latitude on Earth or altitude above the horizon Right Ascension: hours, minutes, & seconds east of the vernal equinox (where the celestial equator and ecliptic cross one another) *like longitude on Earth

Zodiac Constellations: 12 constellations through which the sun passes in a years time (found along ecliptic) Circumpolar Constellations: constellations that can be seen throughout the year at your latitude (“circle the pole”)

How do we locate the planets? All planets orbit within a few degrees of the ecliptic Superior Planets (Jupiter – Neptune) can generally be seen any night, except when on the opposite side of the sun Generally move eastward in celestial sphere from night to night Retrograde Motion – occasional westward motion due to Earth “overtaking” the planet in its orbit

Planets – December 2008

Visible in the morning sky Planets – April 2009 Visible in the morning sky

Properties of Stars Can be measured in terms of diameter, mass, brightness, energy output (power), surface temperature, & composition Diameters: range from 0.1 times the Sun’s diameter to 100 times larger Mass: ranges from 0.01 to 20 or more times the Sun’s mass…some are 50 – 100 times the Sun’s mass but are extremely rare

Apparent Magnitude: how bright a star appears to be. Ranges from 1st – 6th magnitude, 1st is 100 times brighter than 6th Difference of 1 magnitude corresponds to a factor of 2.512 in brightness Does not take into account the distance of the star

Absolute Magnitude: the brightness of an object if they were all lined up at the same distance away Changes the scale a bit since distance is taken into account Sun is brighter than Sirius on apparent magnitude scale, but less bright on absolute magnitude scale Determine distance using parallax – apparent shift in position of star caused by motion of observer

Luminosity: total amount of energy given off by a star Depends on distance and magnitude Extremely wide range (millions of times greater than the sun to thousands of times less than the sun) Composition: Hydrogen and Helium make up 98% of all stars 1 – 2 % Oxygen, Carbon, Nitrogen, Calcium

(Oh Boy An F Grade Kills Me!) Temperature: determined by star’s spectrum (hotter the star, greater the ultraviolet and less the infrared rays) Spectral classes: O, B, A, F, G, K, M (Oh Boy An F Grade Kills Me!) O is the hottest and M is the coolest Each class is divided into 10 subdivisions labeled 0 to 9 (a B1 star is hotter than a B8 star)

H-R Diagrams Hertzsprung – Russell Diagrams compare luminosity and temperature Main sequence stars (80-90%) trend from faint, cool stars in lower right to hot, bright stars in upper left Giants and Supergiants - located above main sequence White dwarfs – stars located below the main sequence Largest stars in the upper right and smallest stars in the lower left Five Luminosity Categories: I. supergiants, II. bright giants, III. giants, IV. subgiants, V. main sequence Our Sun is a G2V star

Stellar Evolution Mass: determines type of length of the life of a star The more massive a star, the shorter its life will be Stages of Life: Nebulas: begin as huge clouds of gas and dust Protostar: gravity causes nebula to contract or collapse on itself forming a disk shape During early stages, not yet hot enough for nuclear fusion & emits no visible light Core temperatures finally reach 8-10 million Kelvins, high enough for nuclear fusion & star is “born” Hydrogen is converting to Helium

A - North American Nebula - emission nebula B - Jewel Box open cluster C - Globular Cluster 47 Tucanae D - Cygnus Loop - supernova remnant

Three main evolutionary paths based on initial mass of star 1st Path: (0.1 to 8 solar masses) Main Sequence – lifetime determined by amt of fuel available & rate of consumption Greater the star’s mass the faster it burns up its fuel & the shorter the time it will be a main sequence star Some stars spend 90% of life as main sequence star

Planetary nebula: expanding shell of gases expelled into space Red Giant: star is running out of hydrogen fuel, cools, gets bigger and becomes more luminous Helium flash occurs at red giant stage that many only last a few minutes/seconds, star shrinks briefly than resumes red giant status Planetary nebula: expanding shell of gases expelled into space Gases keep expanding until they dissipate in interstellar space Core star left, but center becomes white dwarf. White dwarf: small star (about size of Earth), super dense, very high temperatures. Cools over billions of years to become black dwarf Some can become supernova

2nd Path: stars 8 – 25 solar masses Main sequence: much shorter than for smaller stars, more fuel but consumed at a faster rate Red Supergiant: larger and more luminous Supernova: star that blows off its outer shell into interstellar space, luminosity soars & may outshine entire galaxy Estimates show 1 supernova per galaxy every 25-100 years…we have never observed a supernova in our galaxy with a telescope Neutron Star: small (about size of large city), compact stars Can give rise to pulsars – rapidly rotating stars that give off pulses of energy

3rd Path: stars 25 – 130 solar masses Main Sequence: consume fuel at a much faster rate than any of the previous stars Red Supergiant: similar to red supergiants for path 2 Supernova: referred to as Type II supernova for paths 2 and 3 Black Hole: density so high that escape velocity of star becomes equal to the speed of light, so even light cannot escape